Modulating retinoid X receptor with a series of (E)-3-[4-hydroxy-3-(3-alkoxy-5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalen-2-yl)phenyl]acrylic acids and their 4-alkoxy isomers.

Rexinoids are ligands for the retinoid X receptor (RXR) that have great promise for both the prevention and treatment of cancer and metabolic diseases. In this regard, synthetic, functional, and structural investigations into the structure-activity relationships of derivatives of the potent RXR agonist (E)-3-[3-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydronaphthalen-2-yl)-4-hydroxyphenyl]acrylic acid (CD3254, 9) have been conducted. We recently reported on the characterization of a series of C3'-substituted alkyl ether analogues of 9 (10a-f), which display activities ranging from partial agonists to pure antagonists. The importance of the position of the alkoxy side chain for ligand activity has been further explored with the synthesis of C4'-substituted analogues (11a-f). Here we describe the synthesis of compounds 11a-f, which appear functionally different from their isomeric counterparts, as judged from transactivation assays and fluorescence anisotropy experiments. We also report on the 2.0 A resolution structure of RXR in complex with the parent compound 9, which helps understanding of the impact of the alkyl side chain location on ligand activity.

Nuclear receptor ligand-binding domains: reduction of helix H12 dynamics to favour crystallization.

Crystallization trials of the human retinoid X receptor alpha ligand-binding domain (RXRalpha LBD) in complex with various ligands have been carried out. Using fluorescence anisotropy, it has been found that when compared with agonists these small-molecule effectors enhance the dynamics of the RXRalpha LBD C-terminal helix H12. In some cases, the mobility of this helix could be dramatically reduced by the addition of a 13-residue co-activator fragment (CoA). In keeping with these observations, crystals have been obtained of the corresponding ternary RXRalpha LBD-ligand-CoA complexes. In contrast, attempts to crystallize complexes with a highly mobile H12 remained unsuccessful. These experimental observations substantiate the previously recognized role of co-regulator fragments in facilitating the crystallization of nuclear receptor LBDs.